1. Field of the Invention
This invention relates to an electrophotographic photoconductor comprising a pyrene-ring-containing olefin compound in a photoconductive layer thereof, the pyrene-ring-containing olefin compound, an intermediate for synthesizing the olefin compound and a method of synthesizing the olefin compound.
2. Discussion of Background
Conventionally, inorganic materials such as selenium, cadmium sulfide and zinc oxide are used as photoconductive materials of an electrophotographic photoconductor in an electrophotographic process. The electrophotographic process is one of the image forming processes, through which the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity, for instance, by corona charging. The uniformly charged photoconductor is exposed to a light image to selectively dissipate the electric charge of the exposed areas, so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed to a visible image by a developer comprising a coloring agent such as a dye and a pigment, and a binder agent such as a polymeric material.
Fundamental characteristics required for the photoconductor in such an electrophotographic process are: (1) chargeability to an appropriate potential in the dark, (2) minimum dissipation of electric charge in the dark, and (3) rapid dissipation of electric charge when exposed to the light.
However, while the above-mentioned inorganic materials have many advantages, they have several shortcomings from the viewpoint of use in practice.
For instance, a selenium photoconductor, which is widely used at present, completely satisfies the above-mentioned requirements (1) to (3), but it has the short-comings that its manufacturing conditions are difficult to control, and accordingly its production cost is high. In addition, it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to heat and mechanical shocks that it must be handled with the utmost care.
A cadmium sulfide photoconductor and a zinc oxide photoconductor can be easily obtained by coating a dispersion of cadmium sulfide particles and zinc oxide particles in a binder resin on a support. However, they are poor in mechanical properties, such as surface smoothness, hardness, tensile strength and wear resistance. Therefore, they cannot be used in the repeated operation, as they are.
To solve the above-mentioned problems of the inorganic materials, various electrophotographic photoconductors employing organic materials are proposed recently and some are put to practical use. For example, there are known a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on, as disclosed in U.S. Pat. No. 3,484,237; a photoconductor prepared by sensitizing poly-N-vinylcarbazole with a pigment of pyrylium salt, as disclosed in Japanese Patent Publication 48-25658; a photoconductor comprising as the main component an organic pigment, as disclosed in Japanese Laid-Open Patent Application 47-37543; a photoconductor comprising as the main component an eutectic crystal complex of a dye and a resin, as disclosed in Japanese Laid-Open Patent Application 47-10735; a photoconductor prepared by sensitizing a triphenylamine compound with a sensitizer pigment, as disclosed in U.S. Pat. No. 3,180,730; a photoconductor comprising an amine derivative as a charge transporting material as disclosed in Japanese Laid-Open Patent Application 57-195254, a photoconductor comprising poly-N-Evinylcarbazole and an amine derivative as a charge transporting material, as disclosed in Japanese Laid-Open Patent Application 58-1155, and photoconductors comprising as a photoconductive material a polyfunctional tertiary amine compound, especially a benzidine compound, as disclosed in U.S. Pat. No. 3,265,496, Japanese Patent Publication 39-11546 and Japanese Laid-Open Patent Application 53-27033.
Although the above photoconductors have excellent characteristics and can be used in practice, they are still unsatisfactory as photoconductors for use in electrophotography.
As the conventional methods for synthesizing olefin compounds, various methods are reported, for instance, in "K. B. Becker; SYNTHESIS 341 (1983)". In particular, as the methods of sysnthesizing pyrene-ring-containing olefin compounds, method (1) utilizing Grignard reaction, method (2) utilizing an Anil synthesis, method (3) utilizing Knoevenage reaction, method (4) utilizing Wittig reaction, and method (5) utilizing Wittig-Horner reaction are described in the above reference.
More specifically, as an example of method (1), styryl pyrene is synthesized by use of benzyl magnesium chloride and formic acid as disclosed in "Rec. trav. chim., 74, 119(1955). As an example of method (2), a method of synthesizing 1-(2-naphthyl)-2-(3-pyrenyl)ethylene is disclosed in "C.A. 71, 71927". As an example of method (3), a method of synthesizing 1-(2,4,6-trinitrostyryl)pyrene from the reaction of pyrene-1-aldehyde and 2,4,6-trinitrotoluene is disclosed in German Laid-Open Patent Application 2,513,190 (1975). These methods (1) to (3), however, have the drawbacks that the reaction conditions are difficult, for instance, the reaction must be carried out in a dehydrating condition at high temperatures, taking a lot of time, and the compounds that can be employed are limited to compounds which are activated by electron attractive substituents.
By sharp contrast to the above methods, method (4) which uses a phosphorous compound is an excellent method for synthesizing olefin compounds under mild conditions. More specifically, this reaction provides olefin compounds by the reaction between phosphonium ylide and carbonyl compounds. For example, Bull. Chem. Soc. Jpn. 44 2231 (1971) and 45 875 (1972) describe a Wittig reaction utilizing as a Witting reagent pyrenyl methyl triphenylphosphonium bromide, which provides olefin compounds which are related to the olefin compound according to the present invention. As mentioned above, this reaction is excellent in the production of the olefin compounds. However, the olefin compound obtained by this reaction is a mixture of cis- and trans-olefin compounds, so that it has the shortcomings that the reactivity of those olefin compounds with certain ketones is low and that it is difficult to eliminate phosphine oxide produced as a side product in an amount equimolar to that of the olefin compound produced.
As an example of method (5), a method of synthesizing a substituted aminostyryl pyrene by the reaction of pyrene aldehyde and diethyl 4-diphenylaminobenzylphosphonate is disclosed in Japanese Laid-Open Patent Applications 1-252965 and 1-253753. It is considered that this method is extremely difficult to carry out for use in practice.